In conventional air-conditioning apparatuses which perform cooling, heating, and dehumidification (to be collectively referred to as “air-conditioning” hereinafter) of a room or the like (air-conditioned space), an indoor unit and an outdoor unit are connected to each other through a refrigerant pipe and an electric wire. In such an air-conditioning apparatus, a refrigerant circuit is formed using, as its main components, a compressor, an outdoor heat exchanger, an expansion mechanism, an indoor heat exchanger, and a four-way valve. The air-conditioning apparatus performs desired air-conditioning while switching the direction in which a refrigerant sent from the compressor circulates, by the operation of the four-way valve, using a heat pump (refrigeration cycle).
As such an air-conditioning apparatus, multi-unit air-conditioning apparatuses in which a plurality of indoor units are connected to a single outdoor unit by pipes have been known. Multi-unit air-conditioning apparatuses include an apparatus in which indoor units are able to independently perform an automatic cooling and heating operation and an apparatus in which indoor units are unable to independently perform an automatic cooling and heating operation. In the former air-conditioning apparatus, the indoor units are able to independently, selectively perform a cooling or heating operation. In contrast, the latter air-conditioning apparatus needs to select cooling or heating for all the indoor units, and be operated as a whole in the selected operation mode. Therefore, there is a challenge as to how to determine the operation mode of the air-conditioning apparatus. In particular, in an automatic operation mode in which either cooling or heating is automatically determined and performed, if the determination operation is done based on the states of individual indoor units, different determination results may be obtained. For the above-described reasons, it has generally been said that automatic operation control is difficult in multi-unit air-conditioning apparatuses. For example, frequent switching between cooling and heating may cause an unstable operation. Further, the change in room temperature may be large, resulting in a low-efficiency operation.
In order to solve such problems, for example, an air-conditioning apparatus is available, in which a plurality of indoor units perform operation in either a heating operation mode or a cooling operation mode. In this air-conditioning apparatus, for at least one set of indoor units of the plurality of indoor units, two temperatures are set such that the indoor temperature is controlled to fall within the range between the two set temperatures. The entire system can be switched to cooling or heating in accordance with the difference between the indoor temperature and each of the set temperatures of each of the indoor units. Further, for another set of indoor units of the plurality of indoor units, one temperature is set and the indoor temperature is controlled to be close to the set temperature, so that both comfort and energy conservation can be attained (see, for example, Patent Literature 1).
Also, even when the indoor environment in which a master unit is installed is significantly different from that in which a slave unit is installed, air-conditioning is performed in an operation mode corresponding to the indoor environment for the master unit. In order to solve a problem that a comfortable air-conditioning environment cannot be provided in a room in which a slave unit is installed, an air-conditioning system providing an operation control method and program for a multi-unit air-conditioning apparatus has been proposed, which is capable of providing a comfortable air-conditioning environment by selecting a suitable operation mode when an automatic operation mode is set (see, for example, Patent Literature 2).